Here is an example of the problem (after the rough patch on T85356 is applied)

$ python pwb.py scripts/harvest_template.py -family:wikipedia -lang:test -template:test test P404 -simulate
WARNING: cacheSources: Could not load sources: Page [[wikidata:test:Wikidata:List of wikis/python]] doesn't exist.
Finding redirects...
Retrieving 9 pages from wikipedia:test.
WARNING: API warning (wbgetentities): Unrecognized value for parameter 'sites': testwiki
ERROR: param-missing: A parameter that is required was missing (Either provide the item "ids" or pairs of "sites" and "titles" for corresponding pages)
Traceback (most recent call last):
  File "./pywikibot/bot.py", line 1190, in run
    item = pywikibot.ItemPage.fromPage(page)
  File "./pywikibot/page.py", line 3251, in fromPage
    if not lazy_load and not i.exists():
  File "./pywikibot/page.py", line 2867, in exists
    self.get()
  File "./pywikibot/page.py", line 3263, in get
    super(ItemPage, self).get(force=force, *args, **kwargs)
  File "./pywikibot/page.py", line 2901, in get
    data = self.repo.loadcontent(identification, *args)
  File "./pywikibot/site.py", line 5173, in loadcontent
    data = req.submit()
  File "./pywikibot/data/api.py", line 1093, in submit
    raise APIError(code, info, **result["error"])
APIError: param-missing: A parameter that is required was missing (Either provide the item "ids" or pairs of "sites" and "titles" for corresponding pages)

Is this still a problem? If not, can it be resolved?

In T85358#1392985, @zeljkofilipin wrote:

Is this still a problem? If not, can it be resolved?

The steps to reproduce the problem still produce the same error.

Removing browser-tests, I do not think it is related. Please add it back if you think it is.

So now this is a regular problem on pywikibot integration tests.
https://travis-ci.org/wikimedia/pywikibot-core/jobs/75715391#L1153

The test that is failing is test_unconnected in https://github.com/wikimedia/pywikibot-core/blob/master/tests/site_tests.py

1. It loads https://test.wikipedia.org/wiki/Special:UnconnectedPages
2. In the travis job error above it starts working on the first page on Special:UnconnectedPages, which is "Most-perfect magic square/invited"
3. It loads the data repository for test.wikipedia, which is configured to be test.wikidata (see https://test.wikipedia.org/w/api.php?action=query&meta=wikibase)
4. Tries to detect whether the page is indeed not linked to an item in the data repository using https://test.wikidata.org/w/api.php?format=json&action=wbgetentities&sites=testwiki&titles=Most-perfect%20magic%20square/invited
5. The API responds with

{"servedby":"mw1017","warnings":{"wbgetentities":{"*":"Unrecognized value for parameter 'sites': testwiki"}},"error":{"code":"param-missing","info":"A parameter that is required was missing (Either provide the item \"ids\" or pairs of \"sites\" and \"titles\" for corresponding pages)","messages":[{"name":"wikibase-api-param-missing","parameters":[],"html":{"*":"A parameter that is required was missing"}}],"*":"See https://test.wikidata.org/w/api.php for API usage"}}

testwiki isnt a wiki listed as a valid value for sites: https://test.wikidata.org/w/api.php?action=help&modules=wbgetentities

The only test wiki which is listed as a value value for sites is : testwikidatawiki

Change 231764 had a related patch set uploaded (by John Vandenberg):
Wikibase integration tests fail on test.wikipedia

https://gerrit.wikimedia.org/r/231764

Change 231764 merged by jenkins-bot:
Wikibase integration tests fail on test.wikipedia

https://gerrit.wikimedia.org/r/231764

Adding a link at least works on test.wikpedia.org but this won't add a link for the site the link was made from.
Example:
On https://test.wikipedia.org/wiki/Blablabla i added https://de.wikipedia.org/wiki/Hauskatze but this created the item https://test.wikidata.org/wiki/Q1734 which links to https://en.wikipedia.org/wiki/Blah instead of testwiki.

Yes, it seems testwiki and test2wiki have an interesting configuration.

Preferred way of testing would be unit tests that don't talk to a mediawiki installation.
With what I wrote in T58961#1718288 you would get a job with a wiki, but as Wikibase doesn't work out of the box it needs additional commands to configure. In addition you'd need another wiki as a client. So that way would be a bit more work.
For local testing against a mediawiki the wikidata vagrant role should work out of the box (you get a wikifarm with an additional wikibase client wiki and repo wiki).

Have T94416 fixed this?